Vehicle emission control systems may be configured to store fuel vapors from fuel tank refueling and diurnal engine operations in a fuel vapor canister, and then purge the stored vapors during a subsequent engine operation. The fuel vapors may be stored in the fuel vapor canister, which contains adsorbent material, such as activated carbon, capable of adsorbing hydrocarbon (HC) fuel vapor. A concentration of stored vapors in the fuel vapor canister may be assessed, e.g., as a load of the fuel vapor canister, based on purging and refueling events. If the fuel vapor canister is not purged periodically, stored fuel vapors may break through and reduce emissions compliance of the vehicle.
One example approach to determining the load of the fuel vapor canister includes utilizing output from exhaust gas sensors. Specifically, output from exhaust gas sensors is monitored when the fuel vapor canister is purged and stored vapors are combusted in the engine. Another example approach includes determining canister loading based on temperature changes within the fuel vapor canister during loading and purging. For example, as fuel vapors flow into the fuel vapor canister for storage, canister temperature increases. Further, when the fuel vapor canister is purged, canister temperature decreases. These changes in canister temperature may be monitored to determine the load of the fuel vapor canister.
The inventors herein have recognized potential issues with the above described approaches. For example, in the approach utilizing output from exhaust gas sensors, the engine has to be operational and combusting purged fuel vapors for determining canister load. However, in hybrid vehicles, the engine may be shut down and may not be operated for substantially long durations. Accordingly, learning an existing load of the fuel vapor canister at a given time may not be feasible without engine operation. If the engine has to be activated to learn the existing load of the fuel vapor canister, fuel economy of the hybrid vehicle is reduced. In the example of using canister temperature to estimate the existing load of the fuel vapor canister, the increase in canister temperature in response to adsorbing fuel vapors may be temporary. As an example, if the vehicle is fueled and parked for a considerable duration, the canister temperature may equalize with ambient temperature even though fuel vapors are stored within the fuel vapor canister. Likewise, canister temperature may decrease in response to a purging operation, but this decrease in canister temperature may fade over time. Accordingly, the canister temperature may be used as an indicator of canister load either during active purging with engine operation or during storing of fuel vapors but not when the engine is non-operational.
The inventors herein have recognized the above issues and have developed approaches to at least partially address these issues. One example approach includes a method for an evaporative emissions system in a vehicle, comprising routing each of a purge flow from a fuel vapor canister, a loading flow into the fuel vapor canister, and a breakthrough flow from the fuel vapor canister through a hydrocarbon sensor, and determining a load of the fuel vapor canister based on output from the hydrocarbon sensor during each of the routings. In this way, the existing load of the fuel vapor canister may be estimated without engine operation.
In another example, a method may comprise adjusting a three-way valve to a first position to flow purge vapors from a canister through a hydrocarbon sensor, adjusting the three-way valve to a second position to flow refueling vapors from a fuel tank into the canister via the hydrocarbon sensor, adjusting the three-way valve to a third position to flow breakthrough vapors from the canister into atmosphere via the hydrocarbon sensor, and determining a load of the canister based on output from the hydrocarbon sensor during each adjusting of the three-way valve. Thus, adsorption of fuel vapors and desorption of fuel vapors from the fuel vapor canister may be utilized to estimate the load of the fuel vapor canister.
As one example, a vehicle may include an engine, a fuel system including a fuel tank, and an evaporative emissions control system including a fuel vapor canister and a hydrocarbon (HC) sensor. A three-way valve may be coupled to each of the fuel tank, the fuel vapor canister, and the hydrocarbon sensor. Further, the three-way valve may be capable of assuming one of multiple positions (e.g., three). During a purging operation, for example, the three-way valve may be placed in a first position that allows purged vapors exiting the fuel vapor canister to flow past the HC sensor before entering an intake manifold of the engine for combustion. During a refueling event, the three-way valve may be adjusted to a second position to enable the flow of fuel vapors released from the fuel tank into the fuel vapor canister. Further, fuel vapors exiting the fuel tank may be routed past the HC sensor before entering the fuel vapor canister. During an engine-off mode, such as when the vehicle is parked and no refueling event is occurring, the three-way valve may be adjusted to a third position wherein if fuel vapors breakthrough from the fuel vapor canister, these breakthrough vapors are routed through the HC sensor before escaping into the atmosphere. As such, the HC sensor measures an amount of fuel vapors flowing past during each of the purging operation, the refueling event, and vapor breakthrough conditions. The existing load of the fuel vapor canister may be determined based on the amounts of fuel vapors sensed by the HC sensor during each of the purging operation, the refueling event, and vapor breakthrough conditions.
In this way, an existing load of the fuel vapor canister may be estimated. A single common HC sensor may be used to measure each of a quantity of fuel vapors entering the fuel vapor canister and a quantity of fuel vapors exiting the fuel vapor canister during distinct engine conditions. The technical effect of using HC sensor output is that the load of the fuel vapor canister may be estimated in a more accurate manner. Further, by using a single, common HC sensor, a reduction in hardware components as well as expenses may be obtained. Further still, the load of the fuel vapor canister may be assessed without activating engine combustion for purging. Thus, fuel vapor canister load may be calculated without adverse effects on fuel economy and efficiency of the vehicle.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.